Certain tests and/or maintenance operations require, in order to carry them out, the power unit to have reached a minimum temperature. For example, tests on a system that injects fuel into the internal combustion engine require the engine, the injection system and the fuel to have reached a respective minimum temperature.
For other tests and/or maintenance operations, these conditions may extend to other auxiliary elements that the power unit comprises, for example a cooling circuit and/or a lubricating circuit of the internal combustion engine, an exhaust line for the exhaust gases leaving the engine, and notably one or more emissions-control elements located in this line, etc.
Prior to these tests and/or maintenance operations, the power unit is therefore warmed up so that at least some elements of this unit reach the temperature required for starting the tests and/or operations.
According to the prior art with reference to FIG. 1, and considering the nonlimiting example of a test on the injectors of the fuel injection system of the internal combustion engine, the method for accelerating the warming-up according to the prior art, referenced 20a in FIG. 1, foresees a step 21 of warming up the unit by keeping the engine at a greatly accelerated idling speed 22.
As soon as this method 20a is begun, the air conditioning is deactivated 36a. This nevertheless presents the disadvantage of not assisting with the accelerated warming-up of the power unit because the engine has not been subjected to any additional torque demand caused by the operation of the air conditioning.
At periodic intervals during the progress of the accelerated warming-up according to the prior art, the question as to whether the warming-up has reached the level required for preceding with the test and/or with a maintenance operation is asked, and this is symbolized by CH ? in FIG. 1. If the answer is yes, symbolized by 0, then the test and/or the maintenance operation is proceeded with, and if the answer is no, symbolized by N, the accelerated warming-up method is continued, repeating step 21.
The reference 23 symbolizes the final conditions representative of completed accelerated warming-up. In the case of a test relating to an injection system, the accelerated warming-up may be considered to have been completed when the coolant temperature in the engine cooling circuit and the fuel temperature are higher than a respective value that can be calibrated.
The method then proceeds to start the test and/or the maintenance operation referenced 25. The specific conditions for carrying out the test and/or the maintenance operation 25, for example, but not necessarily, a specific fuel pressure, are referenced in 26.
The combustion settings employed during this accelerated warming-up according to the prior art are the standard or nominal settings which are selected to reduce pollutant emissions in the exhaust gases and fuel consumption and which are therefore unfavorable with regards to increasing the temperature of the power unit.
Such an accelerated warming-up according to the prior art prior to commencing the test and/or the maintenance operation therefore often lasts too long, more particularly when the external temperature is low.
That requires the vehicle to be immobilized for a lengthy period of time at the site at which the vehicle is kept stationary and therefore occupies the test and/or maintenance operation facilities for all the time for which the vehicle power unit has not reached the required temperatures specific to the test and/or to the maintenance operation. It then follows that the test and/or the maintenance operation cannot always take place or may sometimes have to be interrupted through lack of time.
In addition, because the prior accelerated warming-up takes a long time according to the prior art, maintaining a greatly accelerated idling speed, for example of the order of 2500 revolutions per minute, for a long period of time, is uncomfortable for personnel located in the external environment of the vehicle to withstand, given the noise caused by this accelerated idling speed.
As an idea of the figures involved, starting from an outside temperature of −10° C., such accelerated warming-up according to the prior art makes it possible to reach a coolant temperature desired for the test and/or operation in 30 minutes or to arrive at a desired fuel temperature in 50 minutes, this or these temperatures being required for commencing most tests and/or maintenance operations. These lengths of time are too long and need to be shortened.
Document DE-A-10058057, incorporated by reference herein, describes a method for rapidly warming up a combustion engine during a phase of starting a rolling vehicle. That document therefore does not describe accelerated warming-up of a power unit of a stationary vehicle prior to a test and/or maintenance operation, although its teaching can be adapted to such warming-up.
The objective of the warming-up sought in that document is to activate the phase of starting of an internal combustion engine. To accelerate the warming-up, provision is made for the delivery of fuel compressed by the injection system to be increased. Furthermore, provision is made for this increased fuel delivery not to be injected into the internal combustion engine but to be used as a heat source for warming up the engine cooling circuit, this being done by way of a heat exchanger exchanging heat between the fuel and the coolant positioned in a return circuit returning the fuel to a fuel tank.
Such a method presents the disadvantage of increased fuel consumption and non-uniform warming-up of the engine since the injectors for example are heated little if at all by the additional quantity of fuel which is not injected into the engine.